Uncounted loop vectorization example doesn't work with unsigned index

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Project / Subsystem

gcc / gcc

Date

2026-05-08

Proposer

Ionuț Nicula <nicula@nicula.xyz>

Source type

public_inbox

Consensus

Proposed

Sentiment

—/10

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All attributes

project: gcc
subsystem: gcc
patch_id: —
discussion_id: RBlv2bEIAjMT7EObrykvjwAIayfw7zt694lcYZussS7znSTokffPSGSvvkr5BMTNeJDwORowmtXj12FGWUoHrFkt6fgv2O_aUQEsMOX3Cdk=@nicula.xyz
source_type: public_inbox
title: Uncounted loop vectorization example doesn't work with unsigned index
headline: Uncounted loop vectorization example doesn't work with unsigned index
tldr: The uncounted loop vectorization in GCC 16 doesn't work with unsigned loop indexes in the example.
proposer: Ionuț Nicula <nicula@nicula.xyz>
consensus: Proposed
outcome: proposed
sentiment_score: —
technical_tradeoffs: []
series_id: —
series_role: standalone
series_parts: []
tags: []
url: https://inbox.sourceware.org/gcc/RBlv2bEIAjMT7EObrykvjwAIayfw7zt694lcYZussS7znSTokffPSGSvvkr5BMTNeJDwORowmtXj12FGWUoHrFkt6fgv2O_aUQEsMOX3Cdk=@nicula.xyz
bugzilla_url: —
date: 2026-05-08T00:00:00.000Z

Uncounted loop vectorization example doesn't work with unsigned index

Ionuț Nicula reports that the uncounted loop vectorization example in GCC 16 fails when using an unsigned type for the loop index, while working correctly with signed integers. This may be a limitation in the current implementation. Users who rely on loop vectorization with unsigned indexes should be aware of this limitation.